Electrostatic spray coating apparatus



Oct. 5, 1965 K. H. LIEDBERG ETAL ,2

ELECTROSTATIC SPRAY COATING APPARATUS Filed Feb. 16, 1962 2 Sheets-Sheetl 5/ 50 a, a Z

ATTORNEY Oct. 5, 1965 K. H. LIEDBERG ETAL 3,210,008

ELECTROSTATIC SPRAY COATING APPARATUS Filed Feb. 16, 1962 2 Sheets-Sheet2 i I i i l I INVENwES I (avfle /wax LkJeg-f g-gf Ddrlan Fame pafiu-san.

United States Patent Sweden Filed Feb. 16, 1962, Ser. No. 173,633 10Claims. (Cl. 239-15) This invention relates to spray coating apparatusand more particularly to an electrostatic spray coating apparatus foratomizing and charging particles of coating material for use inelectrostatic liquid coating deposition systems incorporating anelectrostatic field created between the article to be coated and theissuing source of the coating material. As a such issuing source theinvention features a gaseous pressure fluid driven spray gun.

One object of the invention is to provide an electrostatic spray coatingapparatus which works on the principle of atomization of the coatingmaterial with the help of a gaseous pressure fluid and simultaneouselectrical charging of the material, the gun being provided withimproved means for performing said charging in connection with theatomization. Another object of the invention is to provide anelectrostatic spray coating apparatus of the above character withprojection of a jet of liquid particles into the atmosphere via a mixingchamber for the jet placed under high electrostatic tension in order toretard and efficiently charge said particles. A further object of theinvention is to provide an electrostatic spray coating apparatus of theabove character in which the particles of the jet receive an additionalretardation and charging by means of a secondary electrode in the pathof said jet. A still further object of the invention is to provide, inan electrostatic spray coating apparatus of the above character, arotatable mixing chamber or a rotatable spray nozzle under high tensionfor rotating the jet and thereby retarding the projected particles ofsaid jet.

The above and other objects of the invention will become obvious fromthe following description and from the accompanying drawings, in whichthree embodiments of the invention are illustrated by way of examples.It should be understood that these embodiments are only illustrative ofthe invention and that various modifications may be made within thescope of the claims without departing from the scope of the invention.

In the drawings, wherein like parts are designated by like referencecharacters throughout the several views,

FIG. 1 is a sectional side view of an electrostatic spray coating gunaccording to the invention,

FIG. 2 is a nozzle end view of the spray gun in FIG. 1,

FIG. 3 is a sectional side view of the nozzle end of a modified spraygun according to the invention,

FIG. 4 is a sectional diagrammatic side view of the nozzle end ofanother modification of the spray gun, viewed substantially on line 44in FIG. 5 but omitting some of the needle bearings, and

FIG. 5 is a section on line 5-5 in FIG. 4.

The spray coating apparatus in FIG. 1 incorporates a body portion orbarrel portion of electrically insulating material carried by aconventional body 11 of a spray gun provided with a hand grip 12 and aninlet 13 for gaseous pressure fluid such as air. The apparatus is alsoprovided with a liquid inlet 14 for fluent or liquid coating materialand a trigger 15 for controlling by means of a valve 16 the delivery ofair from the inlet 13 to the body portion 10. The trigger 15 is alsoarranged to control the discharge of liquid coating material bydisplacing a spindle 17 of insulating material in rearward 3,219,008Patented Oct. 5, 1965 direction against the action of a return spring'18 interposed between a sleeve 20 and the spindle 17. The rate ofretraction of the spindle 17 maybe set by an adjusting nut 19cooperating with a threaded portion of the sleeve 20, which is slidablybut unrotatably-arranged in the body 11 and forms an axial abutmentfor'the spindle 17. The forward end of the body 11 receives a bushing 21of insulating material, preferably of nylon, to the interior of whichthe liquid inlet 14, which may incorporate a nylon nipple, is connected.The spindle 17 extends through a plug 22, which is threadedly receivedin the bushing 21 and compresses a tubular sealing member 23 tightlybetween the bushing 21 and the spindle 17. To the forward end of thebody 11 is also threaded a coupling ring 24 for securing the 'gun bodyportion 10 to the body 11.

The body portion 10 consists of an inner tube 25, hollow end pieces 26,27 threadedly secured to the ends of the inner tube 25, and an outertube 28 extending between and tightly connected to the end pieces 26, 27and surrounding the inner tube with some play. All these parts 25-28forming the body portion 10 are of electrically insulating material,preferably of nylon. The rear end piece 27 has a circumferential flange29 and is tightly centered by means of rear conical surfaces 30 in acentering collar 31 nested in the forward end of the body 11 and tightlysurrounding the bushing 21. The end piece 27 is also threadedly receivedin the bushing 21 and the clamping ring 24 coacts with thecircumferential flange 29 for keeping the rear end piece 27 and thecentering collar 31 firmly attached to the body 11, thereby keeping theentire body 10 secured to said body 11. The spindle 17 extends forwardlythrough the bushing 21 and the body portion 10. Around the spindle 17there is formed an annular central passage 32 for conveying the liquidcoating material to the nozzle end of the body portion 10. The air inlet13 is connected over a passage containing the control valve 16, to anannular chamber 33 formed in the body 11 around the bushing 21 andtightly closed by the centering collar 31. From the chamber 33 the airpasses through axial passages 34, 35 in the collar 31 and the rear endpiece 27, respectively, through the space 37 between the tubes 25 and 28of the body portion '10, and thence to the forward end of the front endpiece 26 through axial passages 38 therein.

At the front end of the end piece 26 a hollow nozzle body 39 ofelectrically conductive material is screwed into the piece 26. A centralliquid discharge nozzle 40 is formed in the body 39 and is controlled bya needle valve 41 forming the tip of the axially displaceable spindle17. In the nozzle body 39 there are arranged gaseous pressure fluid orair passages 42 oriented to direct forwardly converging air jets. Ametalliccuplike sleeve or spray nozzle 43 fits coaxially over andsurrounds the discharge end of the nozzle 40 and of the passages 42 andis tightly pressed over and against the nozzle body 39 by a clampingring 44 threadedly secured to the mantle of the front end piece 26.Inside of the clamping ring 44 there is defined an annular air chamber45 receiving air through the passages 38 in the front end piece 26 andcommunicating with the passages 42 of the nozzle body 39. The spraynozzle has a bore or recess, which freely surrounds the outlet tip ofthe liquid discharging nozzle 40, and forms a gaseous pressure fluid orair discharging nozzle '46 around said tip. Downstream of the nozzles 40and 46 the spray nozzle 43 forms a mixing chamber 47 for the jet ofliquid particles formed and projected into the atmosphere by the airdischarging nozzle 46. This mixing chamber 47 is provided with adischarge passage in the form of a transverse spray slot 48 for finallyforming or shaping the cross section of the jet.

Oriented in a plane through the spray slot 43 and through the centralaxis of the body portion and fixed to the spray nozzle 43 are opposedinsulated conductors 49 carrying between their forwardly directed ends asecondary electrode 50 in the form of a fine wire disposed transverselyof and in the path of the jet in front of the spray slot 48, i.e. in theplane of the conductors 49. An electrically insulated oval ring 51, forexample consisting of an insulated wire ring, may extend between. theconductors 49 in order to prevent accidental contact between thesecondary electrode 50 and the object to be coated. Adjacent the innersurfaces of the ring 51 there may be provided supplemental or secondaryelectrode Wires 52 in conductive contact with the conductors 49 in orderto prevent accumulation of coating material from the jet on the ring 51.

The body 11 may be grounded by a wire 54 connected to the hand grip 12.An efficiently insulated high tension conductor 53 is connected to oneof the conductors 49, for example to the spray nozzle 43, for applying ahigh voltage to the conductive nozzles 40, 46 and 43 and the electrodewires 50 and 52.

In operation, the conductor 53 will be connected to a high potentialsource in the form of a suitable conventional electrostatic generator,while the liquid inlet 14 will be connected to a pressurized liquidcoating supply and the air inlet 13 to a compressed air source. Theelectrostatic generator keeps the spray gun nozzles 40, 46, 43 as wellas the electrode wires 50, 52 at a high negative or positive potentialwith respect to the environment, for example at 90,000 volts or more,while the object to be coated is kept at a low potential, for examplegrounded, with respect to the nozzle end of the spray gun. Afterbringing the spray gun to a suitable close distance from the object tobe coated, the operator actuates the trigger 15, thereby retracting thespindle 17 and its tip 41 to a preadjusted extent, whereupon liquidcoating material is fed through the passage 32 and discharged throughthe liquid discharging nozzle 40. Simultaneously compressed air isadmitted to the annular chamber 33 via the valve 16, and passestherefrom through the passages 34, 35, 37 and 38 to the annular chamber45, and thence through the air passages 42 to the air discharging nozzle46 and On to the mixing chamber 47 and the atmosphere. The liquidcoating mate-rial is efficiently atomized in the mixing chamber 47 bythe air jet and the liquid particles are then projected through thespray slot 48, which retards the particles of the jet and defines thefinal cross section of the jet. Obviously, use of internal mixingchamber 47 makes possible efficient atomization at substantially lessthan the air pressure necessary for conventional external pneumaticatomization (perhaps as much as half), and, therefore, there is a markedprimary slowing down or retardation of the particles carried in the jetstream. Such retardation is highly desirable because it gives theelectrostatic field more dominance over the air pressure in transferringthe coating particles. Simultaneously with pneumatic atomizing theretakes place in and adjacent the nozzles 40, 46, 43 and the mixingchamber 47 an electrostatic charging and atomizing due to the highpotential of the nozzles and the corona discharge caused thereby.Subsequently the spray is acted upon electrostatically by the fieldsaround the secondary wire electrodes 50 and 52. The electrode 50 byelectrostatic repulsion produces an additional retardation of the jetand charging of the dispersed liquid particles, whereupon they aredeposited on the object to be coated by the combined action of thecomparatively slow air stream and the electrostatic forces. Obviouslysuch combined action is apt to overcome efficiently irreggularities ofthe electrostatic field at corners and the like of irregularly formedobjects, thereby producing an evenly distributed coating while thesufficient retardation of the air stream results in small coatingmaterial losses to the environment. The clogging tendencies of hithertoknown spraying devices equipped with internal mixing chambers areovercome thanks to the high potential of the spray nozzle, by whichcoating particles tending to accumulate thereon are repelled so that thenozzles are kept clean.

In the modified nozzle portion according to FIG. 3, to be used with ahand grip and body arrangement according to FIG. 1, the secondaryelectrode together with its forwardly protruding carrying conductors areomitted. The conductor 53 is directly connected to the spray nozzle 43.The front piece 26 may be fixedly connected to the outer tube 28 by astop screw 56 and a sealing ring 57 may be inserted to secure tightnessbetween the piece 26 and the tube 28. The modification with respect toFIGS. 1, 2 consists mainly in the provision of multiple forwardlydirected transverse spray slots 58 from the mixing chamber 47, which maybe arranged in parallel, angular, crosswise or other relation withrespect to each other. Use of multiple narrow slots instead of a singlewide slot brings about more efficient atomization at a still lowermixing chamber pressure and the slots 58 serve to finally shape thecross section of the projected jet in a manner to retard the coatingparticles of the jet sufiiciently, so that no further retarding andcharging of the particles by means of secondary electrodes will benecessary.

In the modified nozzle portion according to FIG. 4 the body portion 10consists of an integral nylon tube 60 with a central passage 61 thereinfor the liquid coating material and the spindle 17. Threadedly securedto the outer end of the tube 60 is a metallic nozzle body 62 which iscentered on the tube 60 by a conical surface 63. Adjacent to the surface63 there is formed an annular chamber 64 in the body portion 10. An airpassage 65 supplies the chamber 64 with air. Axial passages 66 extendfrom the chamber 64 through the nozzle body 62 to the forward endthereof adjacent to the mantle of a reduced cylindrical portion 67thereon. On the portion 67 there is formed a liquid discharging nozzle68 having a forwardly directed tip. Rotatably arranged and journalled bymeans of a needle bearing 69 on a cylindrical portion of the nozzle body62 is a metallic spray nozzle 70 fitting over the portion 67 and theliquid discharging nozzle 68 with some axial play and forming aconverging conical air discharging nozzle 71 around the tip of theliquid discharging nozzle 68. The spray nozzle 70 also incorporates amixing chamber 72 downstream of the liquid discharging nozzle 68 for thejet produced by the air discharging nozzle 71.

A flange 73 is provided on the rear of the spray nozzle 70. The flange73 is surrounded by a clamping ring '74 threadedly secured to the body10 and forming a support for the flange 73. Inside of the flange 73 thespray nozzle 70 is provided with turbine blading 75 and in front thereofwith an annular exhaust chamber 76 communicating with the atmospherethrough radial ports 77. The turbine blading 75 forms a motor forrotating the spray nozzle 70 on the nozzle body 62. An axial passage '78is provided in the body 10, through which air may be blown against theturbine blading 75 to rotate the spray nozzle 70. The air to the passage78 may be branched off at a suitable location, for example in the bodyof the spray coating apparatus adjacent to a hand grip according to FIG.1, and may be led through the diagrammatically indicated passages 79 and80 to the passages 78 and 65, respectively. At a suitable location theremay also be provided a valve 81 for regulating the air stream throughthe passage 65 to the, air discharging nozzle 71 independently of theair stream to the turbine blading 75. A radially extending protectivering 82 is provided on the spray nozzle 70 for preventing the turbulentair exhausting from the ports 77 to influence the spray pattern of thejet issuing from the spray nozzles 71 and 70. The jet of liquidparticles projected into the atmosphere from the air discharging nozzle71 receives its final form by a spray slot 83 extending from the mixingchamber 72 for example in a plane through the rotational axis of the ofthe spray gun.

spray nozzle 70 and being directed angularly with respect to therotational axis of the spray nozzle 70.

The conductor 53 may be suitably anchored to the body portion as at 84and has a terminal 85 arranged to slide for charging purposes on therear mantle surface of the spray nozzle 70.

In operation, the nozzle arrangement according to FIG. 4 receives airthrough the passages 79 and 78 so that the spray nozzle 70 will berotated by the turbine blading 75. Thereupon liquid material fed throughthe passage 61 will be discharged through the liquid discharging nozzle68 and atomized in the mixing chamber 72 by the air jet discharged fromthe air nozzle 71, to which the air is led through the passage 80, thevalve 81, the chamber 64 and the passages 66. After having been atomizedin the mixing chamber 72 and charged by the high voltage applied to theconductive nozzles 70, 71, 68 by means of the high tension conductor 53,the jet of dispersed liquid particles is finally formed by anddischarged in a retarded state through the rotating constricted sprayslot 83 into the atmosphere. As a result of the radial deflection theparticles of the jet receive an additional retardation prior todeposition on the object to be coated, which is located in front of thenozzle end Obviously the arrangement may also be used for coating theinner surface of tubular articles.

The embodiments of the invention above described and illustrated in thedrawings should only be considered as examples and the invention may bemodified in several different ways within the scope of the followingclaims.

What we claim is:

1. In an electrostatic spray coating apparatus of the characterdescribed for imparting a coating of charged particles of a material toan object and having a body of insulated material, a liquid materialinlet in said body and a gaseous pressure fluid inlet in said body, thecombination which comprises a liquid discharging nozzle on said body atthe end thereof opposite said liquid inlet, a gaseous pressure fluiddischarging nozzle adjacent said liquid discharging nozzle for atomizingthe liquid discharging therefrom, passages in said body in flowcommunication with said liquid inlet and said liquid nozzle and withsaid gaseous inlet and said gaseous nozzle, a substantially cupshapedelectrically conductive spray nozzle formed over the ends of said liquidand gaseous discharging nozzles defining a mixing chamber for saidatomized liquid particles and for imparting an electrostatic chargethereto before entering the atmosphere, at least one restrictedelectrically conductive jet orifice in said spray nozzle leading to theatmosphere for projecting the charged particles to the object to becoated and for forming the crosssection of said projection, and hightension conductor means for applying said electrostatic charge to saidspray nozzle and said jet orifice.

2. In an electrostatic spray coating apparatus of the characterdescribed for imparting a coating of charged particles of a material toan object and having a body of insulated material, a liquid materialinlet in said body, and a gaseous pressure fluid inlet in said body, thecombination which comprises an electrically conductive liquiddischarging nozzle on said body at the end thereof opposite said liquidinlet, an electrically conductive gaseous pressure fluid dischargenozzle adjacent said liquid dlS- charging nozzle for atomizing theliquid discharging therefrom, passages in said body in flowcommunication with said liquid inlet and said liquid nozzle and withsaid gaseous inlet in said gaseous nozzle, a substantially cup-shapedelectrically conductive spray nozzle formed over the ends of said liquidand gaseous discharging nozzles defining a mixing chamber for saidatomized liquid particles and for imparting an electrostatic chargethereto before entering the atmosphere, at least one restrictedelectrically conductive jet orifice in said spray nozzle leading to theatmosphere for projecting the charged particles to the article to becoated and for forming the cross-section of said projection, and hightension conductor means for applying said electrostatic charge to saidliquid discharging nozzle, said gaseous pressure fluid dischargingnozzle, said spray nozzle, and said jet orifice.

3. Apparatus as recited in claim 2 in which said jet orifice is formedas a slot transverse to said body of in-- sulated material for formingthe cross-section of said projection.

4. In an electrostatic spray coating apparatus of the characterdescribed for imparting a coating of charged particles of a material toan object and having a body of insulated material, a liquid materialinlet in said body and a gaseous pressure inlet in said body, thecombination which comprises .a liquid discharging nozzle on said body atthe end thereof opposite said liquid inlet, a gaseous pressure fluiddischarging nozzle adjacent said liquid discharging nozzle for atomizingliquid discharging therefrom, passages in said body in flowcommunication With said liquid inlet and said liquid nozzle and withsaid gaseous inlet and said gaseous nozzle, a substantially cupshapedelectrically conductive spray nozzle formed over the ends of said liquidand said gaseous discharging nozzles defining a mixing chamber for saidatomized liquid particles and for imparting an electrostatic chargethereto before entering the atmosphere, a slot-shaped electricallyconductive jet orifice in said spray nozzle and transverse theretoleading to the atmosphere for projecting the charged particles to theobject to be coated and for forming the cross-section of saidprojection, said spray nozzle and said jet orifice forming a primaryelectrode, a secondary electrode disposed transversely to the path ofsaid projection and downstream of said jet orifice for retarding saidprojection by repulsing said charged particles therein, and high tensionconductor means for applying said electrostatic charge to said primaryand secondary electrodes.

5. In an electrostatic spray coating apparatus of the characterdescribed for imparting a coating of charged particles of a material toan object and having a body of insulated material, a liquid materialinlet in said body and a gaseous pressure fluid inlet in said body, thecombination which comprises a liquid discharging nozzle on said body atthe end thereof opposite said liquid inlet, a gaseous pressure fluiddischarge nozzle adjacent said liquid discharging nozzle for atomizingthe liquid discharging therefrom, passages in said body in flowcommunication with said liquid inlet and said liquid nozzle and withsaid gaseous inlet and said gaseous nozzle, a substantially cup-shapedelectrically conductive spray nozzle formed over the ends of said liquidand said gaseous discharging nozzles defining a mixing chamber and aprimary electrode for said atomized liquid particles and for impartingan electrostatic charge to said atomized liquid issuing from saiddischarge nozzles, a slot-shaped jet orifice in said spray nozzletransverse to said body leading to the atmosphere for projecting thecharged particles to the article to be coated and for forming thecross-section of said projection, a secondary Wire-shaped electrodedisposed transversely to the path of and in said projection in front ofand spaced apart from said transverse jet orifice for retarding saidprojection by repulsing said charged particles therein, and high tensionconductor means for applying said electrostatic charge to said primaryand secondary electrodes.

6. In an electrostatic spray coating apparatus of the characterdescribed for imparting a coating of liquid to an object and having abody of insulated material, a hand grip portion on said body, triggermeans on said body adjacent said hand grip portion, a liquid materialinlet in said body and a gaseous pressure fluid inlet in said body, thecombination which comprises an electrically conductive liquiddischarging nozzle on said body at the end thereof opposite said handgrip portion, valve means in said liquid discharging nozzle, a spindleof insulating material extending through said body and connected to saidvalve means for controlling the discharge from said liquid dischargingnozzle, said spindle being connected to said trigger means for theactuation thereof, an electrically conductive gaseous pressure fluiddischarging nozzle adjacent said liquid discharging nozzle for atomizingthe liquid discharging therefrom, passages in said body in flowcommunication with said liquid inlet and said liquid nozzle and withsaid gaseous inlet and said gaseous nozzle, second valve means in saidgaseous fluid discharging nozzle and connected to said trigger means forcontrolling the discharge from said gaseous pressure fluid dischargingnozzle, a substantially cup-shaped electrically conductive spray nozzleformed over the ends of said liquid and gaseous discharging nozzlesdefining a mixing chamber for said atomized liquid particles and forimparting an electrostatic charge thereto before entering theatmosphere, at least one restricted jet orifice in said spray nozzleleading to the atmosphere for projecting the charged particles to theobject to be coated and for forming the crosssection of said projection,and high tension conductor means for applying said electrostatic chargeto said liquid discharging nozzle, said gaseous pressure fluiddischarging nozzle, and said spray nozzle,

7. Appartus as described in claim 1 in which the portion of said spraynozzle carrying said jet orifice for forming the said cross section ofthe said projection ofcharged particles is rotatable, and which alsoincludes means for the rotation of said jet orifice with respect to saidbody for rotating said projection with respect to the ambientatmosphere.

8. Apparatus as described in claim 1 in which the axis of said jetorifice is at an angle to the axis of said spray nozzle, and in whichsaid spray nozzle includes means for the rotation thereof and said jetorifice therein with respect to said body for rotating said projectionof charged particles with respect to the ambient atmosphere.

9. Apparatus as described in claim 8 in which said rotating meansincludes a gaseous pressure fluid operated motor connected to said spraynozzle and to said gaseous pressure fluid passages in said bodyproviding flow communication between said gaseous pressure fluid inletand said motor.

10. Appartus as described in claim 6 in which said spray nozzle includesgaseous pressure fluid operated means for the rotation thereof and whichis in flow communication with said gaseous pressure fluid passages insaid body and connected to said trigger means for rotating saidprojection of charged particles with respect to the ambient atmosphere.

References Cited by the Examiner UNITED STATES PATENTS 2,625,590 1/53Peeps 239-15 2,697,411 12/54 Ransburg 239-15 2,809,902 10/57 Ransburg239-15 3,000,574 9/61 Sedlacsik 239-15 3,111,266 11/63 Axelson et al.23,93

EVERETT W. KIRBY, Primary Examiner.

MEYER PERLIN, Examiner.

1. IN AN ELECTROSTATIC SPRAY COATING APPARATUS OF THE CHARACTERDESCRIBED FOR IMPARTING A COATING OF CHARGED PARTICLES OF A MATERIAL TOAN OBJECT AND HAVING A BODY OF INSULATED MATERIAL, A LIQUID MATERIALINLET IN SAID BODY AND A GASEOUS PRESSURE FLUID INLET IN SAID BODY, THECOMBINATION WHICH COMPRISES A LIQUID DISCHARGING NOZZLE ON SAID BODY ATTHE END THEREOF OPPOSITE END LIQUID INLET, A GASEOUS PRESSURE FLUIDDISCHARGING NOZZLE ADJACENT SAID LIQUID DISCHARGING NOZZLE FOR ATOMIZINGTHE LIQUID DISCHARGING THEREFROM, PASSAGES IN SAID BODY IN FLOWCOMMUNICATION WITH SAID LIQUID INLET AND SAID LIQUID NOZZLE AND WITHSAID GASEOUS INLET AND SAID GASEOUS NOZZLE, A SUBSTANTIALLY CUPSHAPEDELECTRICALLY CONDUCTIVE SPRAY NOZZLE FORMED OVER THE ENDS OF SAID LIQUIDAND GASEOUS DISCHARGING NOZZLES DEFINING A MIXING CHAMBER FOR SAIDATOMIZED LIQUID PARTICLES AND FOR IMPARTING AN ELECTROSTATIC CHARGETHERETO BEFORE ENTERING THE ATMOSPHERE, AT LEAST ONE RESTRICTEDELECTRICALLY CONDUCTIVE JET ORIFICE IN SAID SPRAY NOZZLE LEADING TO THEATMOSPHERE FOR PROJECTING THE CHARGED PARTICLES TO THE OBJECT TO BECOATED AND FOR FORMING THE CROSSSECTION OF SAID PROJECTION, AND HIGHTENSION CONDUCTOR MEANS FOR APPLYING SAID ELECTROSTATIC CHARGE TO SAIDSPRAY NOZZLE AND SAID JET ORIFICE.